The invention relates to a fuel injection nozzle for combustion engines of the type having a nozzle body, an injection needle slidably disposed in the nozzle body, and a reservoir space downstream of the injection needle seat.
It is known that the various legislators have established ever higher demands regarding the exhaust emissions from internal combustion engines. This is especially so for unburned hydrocarbons wherein a very low value has been prescribed, which through the prior art injection nozzles can scarcely be achieved. It is further known that after the closing of an injection nozzle after a successful injection, there is remaining fuel in the blind pocket reservoir, which does not take part fully in the combustion and is responsible in large measure for the undesirable hydrocarbon emmissions.
With injection nozzles with a minimum pocket reservoir (DE-OS No. 24 38 014), an abutment body formation effective at the injection nozzle tip is fully dived or extended into the pocket reservoir and there are resultant disadvantages in fuel efficiency and smoke. The remaining cross section between the pocket reservoir walls and the abutment body throttles the flow of fuel too strongly.
With injection nozzles of the so-called seating hole type nozzles (DE-OS No. 27 10 217)--provided with injection holes in the injection needle seat to open, they reduce the hydrocarbon emmission about approximately the half value, however, this form of embodiment is not disposed for an error free construction for series production. Injection nozzles of this kind fail by means of the nozzle tip rubbing off. A further disadvantage results because the strong turning of the combustion field out the slot at the cross section of the needle seat in the tip holes does not provide the full fuel pressure at the injection openings. The injection intensity is thereby reduced.
Good efficiency and smoke value is achieved only with optimal flow comparisons in the fuel nozzle. Thereby, it is furthermore necessary to have a nozzle with bottom pocket reservoirs.
The invention is based upon the problem to minimize the effects of the space in the pocket reservoir adjacent the fuel injection nozzle tip and simultaneously to increase the through flow characteristics at the needle seat.
According to the invention, a movable abutment body is slidably disposed in the injection needle to selectively block and free-up the reservoir space and the opening therefrom. The abutment body and needle are separated by a return spring biasing the abutment body to a position filling the reservoir space. The return spring and the pressure surfaces on the injection needle and abutment body are configured so that the reservoir space is free during initial injection and then the abutment body squeezes out any fuel in the reservoir space, thereby reducing engine hydrocarbon emissions.
Through the movement of the abutment body relative to the injection needle, the pocket reservoir is timely fully filled. To begin the injection, this abutment body is, either by means of the combustion room pressure of the engine, or through the fuel pressure in the pressure space, protruded into the injection nozzle. The pocket reservoir is then free and the fuel can stream unhindered into the tip holes, i.e., injection holes.
At the end of the injection procedure the injection nozzle closes in a normal manner and through the strength of the return spring, the outwardly moving abutment body (with respect to the injection needle) forces the remaining fuel within the pocket reservoir into the combustion room.
An illustrative example of the invention is shown in the drawing and is described in more detail below.